Method for Producing Fluorine-Containing Polymer and Composition

Provided is a method for producing a fluorine-containing polymer with little lot-to-lot variation in weight average molecular weight. The method for producing a fluorine-containing polymer of the present invention relates to a method for producing a fluorine-containing polymer containing a repeating unit of formula (1) and a repeating unit of formula (2), which includes: fluorine-containing monomer synthesis including reacting a diol of formula (3) with at least one selected from the group consisting of unsaturated carboxylic acids, esters of the unsaturated carboxylic acids, acid halides of the unsaturated carboxylic acids, and anhydrides of the unsaturated carboxylic acids, to obtain a composition containing a fluorine-containing monomer of formula (4) as a main reaction product and a fluorine-containing monomer of formula (5) as a minor reaction product; fluorine-containing monomer purification including removing the fluorine-containing monomer of formula (5) from the composition to adjust the amount of the fluorine-containing monomer of formula (5), expressed in parts per million based on the mass of the fluorine-containing monomer of formula (4), to 1500 ppm or less; and polymerization including performing a polymerization reaction of the composition obtained after the fluorine-containing monomer purification to give the fluorine-containing polymer containing the repeating unit of formula (1) and the repeating unit of formula (2),